benameur2020

Superlattices and Microstructures 142 (2020) 106473
Available online 28 February 2020
0749-6036/© 2020 Elsevier Ltd. All rights reserved.
Impact of substrate nature and lm thickness on physical
properties of antimony trisulphide (Sb
2
S
3
) thin lms for
multifunctional device applications
S. Ben Ameur
a , b , *
, B. Duponchel
c
, G. Leroy
b
, H. Maghraoui-Meherzi
d
, M. Amlouk
e
,
H. Guermazi
a
, S. Guermazi
a
a
Research Unit: Physics of Insulators and Semi Insulator Materials, Faculty of Science of Sfax, Road of Soukra Km 3.5, B.P: 1171 3000, Sfax,
University of Sfax, Tunisia
b
Unit� e de Dynamique et Structure des Mat� eriaux Mol� eculaires (UDSMM) EA 4476, Universit� e du Littoral C^ ote d’Opale, 62228, Calais, France
c
Unit� e de Dynamique et Structure des Mat� eriaux Mol� eculaires (UDSMM) EA 4476, Universit� e du Littoral C^ ote d’Opale, 59140, Dunkerque, France
d
Laboratoire de Chimie Analytique et Electrochimie, Faculty of Science of Tunis, Tunis El Manar University, Tunisia
e
Research Unit: Physics of Semi-conductor devices, Faculty of Science of Tunis, Tunis El Manar University, 2092, Tunis, Tunisia
ARTICLE INFO
Keywords:
Antimony trisulphide (Sb
2
S
3
)
Film thickness
Flexible polymer substrate
Hydrophobic surfaces
ABSTRACT
Sb
2
S
3
thin lms were deposited with various thickness on glass and exible polymer Poly-
etherimide (PEI) substrates by simple chemical bath deposition. X-ray diffraction patterns reveal
the formation of polycrystalline lms with orthorhombic structure. The Sb
2
S
3
thin lms grown on
the PEI substrate are rougher. The enhancement of roughness for Sb
2
S
3
/PEI thin lms leads to
improve their hydrophobic character. Furthermore, they show high values of contact angle (CA)
around 162. The absorption coefcient of thin lms is determined to be higher than 10
4
cm
1
.
The band-gap energy has been found to be between 1.6 and 2.1 eV as a function of thickness
which related to the variation of structural defects. Thus, the growth of these lms signicantly
depends on the nature of the substrate and its thickness. The obtained results show that all Sb
2
S
3
on glass and PEI thin lms have potential applications in the self-cleaning windows and solar
cells.
1. Introduction
The fabrication of thin lms for various devices like sensors, solar cells, light-emitting diodes has received immense interest of
scientic community since many years. In general, thin lms are deposited on amorphous substrate (i.e. glass). To overcome the
overweight and rigidity of conventional glass substrates, we have observed an increasing interest in the choice of a specic substrate
that depends on the temperature of deposition and post deposition processing. The use of polymer as a substrate can be introduced in
the preparation of exible displays and electronic devices [1–3]. Recently, the deposition of metal oxides, like ZnO [4,5] and SnO
2
[6],
on a exible substrate has been reported which has received remarkable industrial applications of such devices. Additionally, several
polymers such as polyethylene terephthalate (PET) [7] and polyethylene naphthalate (PEN) [4] are also used as exible polymer
substrates.
* Corresponding author. Faculty of Science of Sfax, B.P: 1171 3038, Sfax, University of Sfax, Tunisia.
E-mail address: [email protected] (S. Ben Ameur).
Contents lists available at ScienceDirect
Superlattices and Microstructures
journal homepage: www.elsevier.com/locate/superlattices
https://doi.org/10.1016/j.spmi.2020.106473
Received 18 November 2019; Received in revised form 25 January 2020; Accepted 27 February 2020

Superlattices and Microstructures 142 (2020) 106473
2
Antimony trisulphide (Sb
2
S
3
) is an interesting coating material due to its suitable optical properties; direct band-gap Eg of about
1.7–2.5 eV and high absorbance coefcients in the visible region (
α ~ 10
4
cm
1
) [8]. These properties make Sb
2
S
3
one of the most
promising candidates for the fabrication of extremely thin absorber in solar cells [9–11]. Several research reports describe the growth
of Sb
2
S
3
thin lms on various substrates such as glass [8], FTO [12] etc; However, the growth of Sb
2
S
3
thin lms on the exible polymer
substrate has never been reported as per our knowledge. The choice of a specic substrate becomes essential in order to support the
deposition temperature higher than the room temperature. Polyetherimide (PEI) can be adopted as an alternative substrate in com-
parison to the conventional glass because of its high glass transition temperature (T
g
¼220 C), excellent optical transparency and
mechanical properties [13]. Temperature is a key factor for the deposition of a material on the polymeric substrates. In this regard, a
low-temperature technique such as chemical bath deposition is considered to be very promising method for exible substrates. S. Shaji
et al. [14] have demonstrated the achievement of high crystalline quality of Sb
2
S
3
thin lms by chemical bath deposition (CBD) at low
temperature. This reported technique is cheaper as compared to other expensive physical deposition processes such as Vacuum
Thermal Evaporation (VTE). Furthermore, CBD is a soft solution process that can produce high-quality thin lms at relatively low
temperature since it is relatively simple, cost-effective and permits easy processing [9,15]. The deposition rate and hence thickness of
the deposited lm can be precisely controlled by varying pH, reaction time, temperature and concentration of the solution.
In the present work, we report the Structural, morphological and optical evolution of Sb
2
S
3
thin lms deposited by the CBD method
as a function of nature of substrate and thickness. Structural parameters and growth orientations are investigated by X-ray diffraction
(XRD). The optical and dispersion parameters are estimated from the UV–Visible absorption spectroscopy. In particular, this article
emphasizes a correlation between the physical parameters and super-hydrophobic character of thin lms. The results obtained with
the CBD deposited Sb
2
S
3
/PEI thin lms suggest their potential applications in the self-cleaning windows and solar panels.
Fig. 1. XRD pattern of Sb
2
S
3
thin lms: (a) Sb
2
S
3
/PEI and (b) Sb
2
S
3
/glass.
S. Ben Ameur et al.

Superlattices and Microstructures 142 (2020) 106473
3
2. Experiments details
Sb
2
S
3
thin lms were prepared on both exible polymer Polyetherimide (PEI) and glass substrates simultaneously, using a simple
chemical bath deposition technique (CBD). The growth of Sb
2
S
3
thin lms is based on the reaction of Sb and S precursors at controlled
temperature T ¼60 C in a weakly acidic bath (pH ¼3.8). The chemical bath containing 650 mg of SbCl
3
was dissolved in 10 ml of
acetone and 25 ml of 1 M Na
2
S
2
O
3
and 65 ml of bi-distilled water. H. Maghraoui-Meherzi et al. [15,16] presented a detailed study on
the chemical bath deposition of Sb
2
S
3
thin lms and the variation of deposition time with the thickness of thin lms which estimated
the thickness of lms by the double weight method. In this present investigation, the thicknesses for lms were found to be 300, 600
and 1300 nm. The different time deposition was ranging from 3 to 30 min. For obtaining lm thickness around 600 nm, the time
deposition was about 10 min. In the text below, we termed A, B, and C for the samples deposited on PEI substrate having thicknesses of
300 nm, 600 nm, and 1300 nm respectively, and we named A’ (300 nm), B’ (600 nm) and C’ (1300 nm) for the samples deposited on
glass substrate.
Thickness 300 nm 600 nm 1300 nm
Sb
2
S
3
/PEI A B C
Sb
2
S
3
/glass A0B0C0
Structural, morphological and optical properties of the prepared Sb
2
S
3
thin lms were investigated. Hence, the structural pa-
rameters and their orientation were studied by means of X-ray diffractometer (Analytical X Pert PROMPD) having Cu-k
α radiation (λ ¼
1.5406 Å). An atomic force microscope (AFM-Brüker Multimode) was used in the contact mode to obtain the morphological infor-
mation. The surface wettability of Sb
2
S
3
was examined through the water Contact Angle (CA) measurements using a contact angle
meter (Micro-Drop analysis DSA 100 M) at ambient temperature. The optical transmittance and reectance were measured by
UV–Vis–NIR spectrophotometer (Shimadzu UV 3100 S) in the wavelength range from 350 to 1600 nm. The optical constants and
dispersion parameters have been estimated from the transmittance and reectance spectra of Sb
2
S
3
thin lms.
Fig. 2. Texture coefcients TC of Sb
2
S
3
thin lms: (a) Sb
2
S
3
/PEI and (b) Sb
2
S
3
/glass.
S. Ben Ameur et al.

Superlattices and Microstructures 142 (2020) 106473
4
3. Results and discussions
3.1. Structural properties
X-ray diffraction patterns of Sb
2
S
3
thin lms deposited on PEI polymer substrate and on glass substrates with different thicknesses
are shown in Fig. 1(a and b) respectively. All peaks were indexed to the standard diffraction planes based on standard JCPDS powder
diffraction data sets (78–1347) and revealed that the prepared thin lms ofSb
2
S
3
are polycrystalline in nature having orthorhombic
structure. No other peaks related to impurities have been observed which indicates the formation of high purity Sb
2
S
3
binary phase.
The XRD patterns of Sb
2
S
3
samples deposited on PEI (Sb
2
S
3
/PEI) showed a broad diffuse peak attributed to the amorphous structure of
the PEI polymer. The samples show different preferential orientations. In general, preferential orientations are in turn affected by the
growth conditions such as lm thickness, temperature, topographical and nature of substrate [10,16,17]. Hence, the preferential
growth orientation of the polycrystalline Sb
2
S
3
thin lms can be estimated from the texture coefcient TC (hkl) calculation using the
following relation [10]:
TCðhklÞ¼IðhklÞ=I0ðhklÞ
N1PIðhklÞ=I0ðhklÞ
(1)
Where, I
(hkl)
is the measured intensity for (hkl) diffracting plane, I
0(hkl)
is the corresponding intensity for a randomly oriented sample
taken from the JCPDS card and N is the number of observed diffraction peaks. The variation of the texture coefcient of all Sb
2
S
3
thin
lms is shown in Fig. 2. Our rst motive is to understand the effect of substrate on the nature of thin lms which is discussed as follows:
It is clear that the substrate nature signicantly affects the general texture and the preferred orientation of the lms. We have noted
a change in the orientation, appearance and disappearance of the preferential growth on a plane. This change can be correlated to the
morphology and the adhesion character of the substrate. To disclose this correlation, the surface properties of PEI and glass substrates
were investigated using the CA measurement which is shown in Fig. 3. It’s clear that the PEI polymer substrate surface (θ ¼76) is more
hydrophobic as compared to the glass (θ ¼50). The variation of the hydrophobicity character is due to the difference in the adhesion
forces (Johannes D. van der Waals forces) between the water and the solid surface. Indeed, it is noted that the PEI substrate has the
lower adhesive character with higher adhesion force (118.8 10
3
N/m) as compared to glass one (96.3 10
3
N/m). Furthermore,
during the lm formation, the interaction between the atoms and the substrate is different for the various substrates. These changes
reect in the thermo-dynamical character of lm formation [17,18]. The extrinsic constraint is another parameter that causes the
different orientations of the lms during their growth due to the interaction between the substrate and the lm. The principal origin of
these constraints is the difference between the coefcients of thermal dilatation of the substrates. The coefcients of thermal dilatation
for the glass and PEI are found to be 9 10
6
(C
1
) and 56 10
6
(C
1
), respectively.
In our second motive, we have investigated the role of lm thickness on the preferential growth of the lms. On the same substrate,
the preferential orientation of lms changes with the thickness of the lms. The change in crystallite preferred orientation of the lms
Fig. 3. Contact angle measurement of PEI, glass substrates and all Sb
2
S
3
thin lms.
S. Ben Ameur et al.

Superlattices and Microstructures 142 (2020) 106473
5
can be explained by the atomic rearrangement of the lms.
Additionally, as the microstructure is extremely important and determines the main properties of thin lms including their elec-
trical, mechanical, and optical characteristics, we have proceeded to determine the microstructural parameters of the prepared Sb
2
S
3
lms. Likewise, from the XRD analysis, we determined the microstrain (ζ) as well as the microstructural parameters such as the average
crystallite size (D) and the dislocation density (δ). So, the full width at half-maximum (β) can be used to estimate the average crystallite
size of all Sb
2
S
3
thin lms using Scherrer’s formula [19]:
D¼0:9λ
βcos θ(2)
Where λ is the wavelength of X-ray source.
The structural defects such as the dislocation density (δ), which is dened as the length of dislocation lines per unit volume of the
crystal, and the microstrain (ζ) induced in the lm due to crystal defects such as lattice dislocations, are calculated from the following
expressions [19]:
δ¼1
D2(3)
Table 1
Micro-structural parameters of all Sb
2
S
3
thin lms on PEI substrate.
sample D (nm) δ (10
3
) nm
2
ζ (10
4
) RMS (nm)
A 74 13.5 8.8 136
B 63 15.8 11.3 116
C 83 12 3.5 90
A0162 6.1 2.8 57
B0138 7.2 2. 9 33
C0102 9.8 1.5 22
Fig. 4. 2D and 3D AFM images of all Sb
2
S
3
thin lms.
S. Ben Ameur et al.